1. Field of the Invention
The present invention relates to a method for supplying a liquid material used for deposition of a thin film by, for example, Atomic Layer Deposition (hereinafter referred to as “ALD”). In particular, the present invention relates to a method for controlling the concentration and flow rate of a material of high vapor pressure.
2. Description of the Related Art
Conventionally, film deposition by ALD is performed at short intervals of 0.1 to 1 second in order to switch the precursor and reactant by opening/closing the valves in the gas supply lines.
This presents the problem of inaccurate flow rate control by the MFC (Mass Flow Controller) used in traditional CVD, etc., due to a large fluctuation in line pressure. Under ALD, therefore, the APR (Auto Pressure Regulator) is used to maintain a constant line pressure, while an orifice, etc., provided at the entrance of the reaction chamber is used to control the flow rate. In other words, while the MFC senses heat transfer inside the controller to control the flow rate at the set level, it requires constant flow because the operating principle of the sensor in the MFC is based on heat transfer, and therefore the MFC cannot be used in ALD and other processes where gas is supplied and stopped frequently. By using the APR, however, accurate flow rate control becomes possible for liquid materials whose vapor pressure is low (not to exceed 1/10 th the supply pressure of carrier gas).